In this three year project we will define the effects of commonly used anesthetic drugs on somatosensory evoked responses (SSERs) so that effects of anesthetics on these responses can be separated from the effects of surgical manipulation of the spinal cord and its blood supply. Correction of severe scoliosis with Harrington rod instrumentation and spinal fusion is sometimes followed by disastrous neurologic complications: paralysis in both legs, loss of bowel and bladder function. We now use SSERs, the brain's electrical responses to stimulation of peripheral nerves, to monitor spinal cord function during spine surgery. Anesthetic agents, while very necessary, alter SSERs in ways that must be differentiated from changes due to surgical manipulation. We hypothesize that several anesthetic drugs affect SSERs in characteristic and dose related ways and that we will be able to identify some agents as affecting SSERs more than others. We will measure the effects of 13 drugs commonly used during anesthesia on amplitudes and latencies of SSER peaks, determining the dose-response relationship for 10 of these agents. Ninety patients coming for surgical correction of spinal deformity will be studied using a Nicolet MED 80 system for monitoring SSERs and Hewlett-Packard physiologic monitoring equipment to document steady state conditions during SSER measurement. Definition of the effects of anesthetic drugs on SSERs is important for three reasons: (1) it will improve the reliability of SSER monitoring as an index of spinal cord function during anesthesia and surgery. (2) it will facilitate the development of SSER monitoring for assessment of brain function during anesthesia. (3) it will shed light on neurophysiologic aspects of anesthetic action.